In a ramp (or inclined plane) problem, the angle of the ramp is the same as the angle the gravity vector makes with the component normal to the ramp.
Here’s how you can be sure this is true: Look at the component of the gravity vector that is perpendicular to the ramp. Imagine that the ramp is horizontal—that is, θ is currently 0. Then the perpendicular component points straight down so that it coincides with Fg. Now start lifting the ramp. As the ramp angle increases, so does the angle between the perpendicular component and the gravity vector. You can see that these two angles have to be the same.